In four-cycle engines having four valves, it is customary to use rocker arms to actuate the valves, which rocker arms are mounted on a common rocker arm shaft. Different rocker arms are thereby required on account of the different position of the valves.
In addition, hydraulic clearance compensation elements which are arranged at the valve-side end of the rocker arms increase its polar moment of inertia. As a result, strengthened valve springs are thereby required which result in a stiffening and possible hardening of the rocker arm shaft.
Moreover, the hydraulic clearance compensation elements which are installed in the rocker arm require a complex pressurized oil supply means having fully machined pressurized oil lines. All the above measures cause great manufacturing expenditure.
The PCT application WO 00/20730 describes a valve timing mechanism for four-cycle engines which is improved compared with the above-described prior art and has the following components:                a rocker arm frame which is configured in one piece from lightweight metal and has two bars which are connected by webs, for accommodating the rocker arms;        hydraulic elements for valve clearance compensation which have an outer piston which is open on one side and has a supporting ball which is configured in one piece at the closed end of said outer piston, and an inner piston which is open on one side, is guided in the outer piston and is connected in flow terms via a spring-loaded ball valve to a high-pressure space of said outer piston;        a steel sheet part which is arranged between the hydraulic element and the rocker arm frame.;        a pressurized oil line which is arranged in the longitudinal extent of the rocker arm frame at the level of the open end of the hydraulic elements;        deep-drawn steel sheet rocker arms which are configured uniformly for all the valves, having a U-shaped cross section and having cylindrical rollers mounted on needle bearings for at least one camshaft, and having a cap for the supporting ball, and having contact elements for the valve stems of the inlet and outlet valves.        
Despite the improvements which are achieved by the above components, numerous requirements with regard to low manufacturing and assembly costs are still not met.